Production of powdered alloys



Patented June 1942 V c V Peter P. AlexandenMarblehead, Mass. I

No Drawing. Application J nuary 9', 1940,

I, Serial No. 313,116

H h V 6 ciaii sulcl, 75-415) This inventi rlelates to thefproductionofgpowdered alloys} and more especially to thepro duction of finely dividedpowdered alloys of the refractory and other metals with one another orwith carbonyiron, nickel and cobalt.

The ,formation of alloys of the refractory metals, is, in, general, wellknown ,and may be brought about, for example, in theelectric furpermitonly the weldingand diffusion of adjacent particles and prevent" thecoagulation and sintering of the particles of the alloy or itsconstituents gintolargermasses. f j

, The variousphasesof the processare carried out, in a relatively simplemanner as follows:

nace. Howeve'nthe production of alloys of these metals in theform offinely divided powders capable of passing, say 2 00 mesh or better, isattended with considerable difficulty. -Generally speaking, the alloysare extremely hard and, when produced according to any known orpreviously used process, take the form atbestof largeparticleswhichimust be 'ground tofproduce the degree offineneSsnecessary (for many industrial purposes, a" diflicult operation.If the metals in The powdered oxide, for example, of one of therefractory metals which is to form a part of -the alloy,ris thoroughlymixed with the alloying metal in powdered form. A powdered metalhydride,forexample calcium hydride, is added to the mixture in sufficient amountto carry out the reactions hereinafter described, the whole beingthoroughly, mixed so that the particles of the temperature raiseduntilthe metal hydride disthe form of line powders aresimply fused ,to-

gether they form large particles or even blocks of extreme hardness,thedifiicultyof reducing the latter toifine'powders being even greater.v

According to the present invention,powdered or betterI are-producedwithout"thefnecessity"of subjecting the same crushing orgrindingoperationsx h The process of the invention does not depend, i forfineness, in size "of the powdered alloysproducedthereby, upon thedegree of preliminary crushing and grindingof the metals entering intothe alloys.; While the process is carried out with powdered andthoroughly mixed materials, nevertheless the particles of the finalalloy are much smaller and more uniform in sizethan those of about inthe processby the decomposition of the initial mixture which, in thepreferredform is ac complished partly by the introduction of one of themetals, into the initial mixture, in the form of an oxidawhichis reducedat a temperature below the fusion temperature of the metal, and

partly through ,tthe formation, during the early,

heating stages iofwthe process, of complex cbrripounds of the othermetal which are reduced or otherwise broken up at 'low temperaturesbelow the point of fusion of either alloying metal.

In orderthatthefine particles of metalltmay uniteto form fitre particlesof alloy, the"procels s is further characterized by the fact that it iscar-f ried out under conditions wherein the atmosphere powdered metalhydride are scattered through the mass of powdered metal" and oxide. 1The powdered charge is' placed in a furnace andthe sociates:formingnascenthydrogen and the metal released from the hydride, theflatterbeing in a nascent state. Inasmuch as the density of cal- ,cium hydrideis '13 andthat of metallic calcium 1.55:,it will be'apparent' thatafter" dissociation the released calcium occupies a larger volume thanthe calcium, hydride. There willtherefore be an expansion of everyparticle whichprevi ouslywas composed of calciumhydride, this expansionpushingthe adjacent particles of metallic oxide and metal together, Atthe same time the largelvolume of evolving hydrogenin the mass producesa further, movement ofthe"particles the, initial powderednmaterials.This is brought towards one another. As the hydrogen evolves infthe massit also reduces the metallic oxide to particles of metal and oxygengthlatter uniting with the hydrogen to formtsteam which is im.- mediatelyreducedby the calcium, the latter unit ing with the oxygen to formcalcium oxide While the hydrogenescapes. V c The density of the calciumoxide ismu'ch greaterthen that of the calcium so that there is now acontraction of the particles which were originally calcium hydride, thecalcium' oxide forming a spongy mass comprising countless ele- 'mentalcrucibles surrounding'the particles of the metals which, duringthecontinued application of 'heat arewelded together and diffuse-[into {oneis highly reducing and free from oxygen, thus preventing surfaceoxidation of the particles of the metals which; being free from oxide,may

weld and difiuse into one another. Moreover, 1 the processischaracterized by the fact that there}, is brought about; duringone phasethereof, a oertain amount of movemeht ofthe metallicpar ticles towardsone another which isaccompanied by the formation of a spongy spacerwhich will another, the presence of the highly reducing hydrogen in themasspreventing the formation of surface'oxides on the metallic particlesso that the welding and diffusion maytak'e place. Sintering ofadjacentparticles of alloy into a spongy mass .or intolarger particlesis prevented by the surrounding calcium oxide.

a further aid to the understandingof t e invention I will now describetheforinat'ion of a specific powdered alloymade inaccordance with theinvention, in this instance titaniurn fcarbide.

Powdered calcium hydride and powdered titanium oxide are thoroughlymixed with powdered carbon, preferably in the iform of 1 lamp black. r

gether, the application of heat being continued until the particles ofwelding titanium and carbon 'diil'use into one another forming finelydivided particles of titanium carbide. The reaction may be expressed asfollows:

Tiz+2CaHz+C=TiC+2CaO+2H2 When the reaction is complete the calcium oxidemay be removed in any well known manner, for example, by leaching,leaving powdered titanium carbide.

As far asI am now aware the process is more or less limited to the useof calcium, strontium and barium hydrides as reducing-spacer-formingagents as other reducing agents, such as aluminum, will readily combinewith one or more of the metals to be alloyed and furthermore the heat ofreaction during the first stage would be so great that the whole masswould be fused. In the case of calcium, strontium and barium hydridesthe heat of reaction is very much lower 50 that the whole process iscarried out below the point of fusion and therefore the material comesin fine solid particles of alloy. It is possible that other reducingspacer-forming agents may be substituted for those enumerated but incommercial operation I prefer to use calcium hydride as the other agentshave no marked advantage over calcium hydride whereas the latter is muchcheaper commercially than barium Or strontium hydrides. Moreover calciumhydride may be prepared according to the method disclosed and claimed inmy prior Patent No. 2,082,134, issued June 1, 1937, it being immaterial,insofar as the must be continued to eflect diffusion of the particlesinto one another will vary in accordance with the metals of the groupwhich are selected to form the alloy.

While I have described my process with great particularity, it will beunderstood that the same may be varied within the spirit of theinvention and the scope of the appended claims.

What I claim is:

l. The process of forming powdered alloys consisting of a metal selectedfrom a first group consisting of titanium, zirconium, tungsten, hafnium,thorium, tantalum, uranium, molybdenum, chromium and beryllium and analloying element selected from a second group consisting of titanium,zirconium, tungsten, hafnium, thorium, tantalum, uranium, molybdenum,chromium, beryllium, carbon, nickel, iron and cobalt which comprisesthoroughly mixing a powdered oxide of the metal of the first group withpowdered calcium hydride and the alloying element of the present methodis concerned, whether or not all traces of magnesium oxide are removed.

There are further apparent limitations of the process, namely, that thealloying metals must combine more readily with one another than with themetal liberated from the reducing-spacerforming agent, thus, while themetals, titanium, zirconium, tungsten, hafnium, thorium, tantalum,uranium, molybdenum, chromium and beryllium may be alloyed with oneanother or with carbon, nickel, iron and cobalt, in accordance with theprocess, they may not be alloyed with silicon, copper and magnesium,which combine and form stable compounds with calcium.

During the early heating stages, before the calcium hydride is reducedto calcium and hydrogen, it is probable that the powdered metal formscomplex compounds with the calcium hydride, these compounds breaking upas the temperature increases. I donot commit myself as to the nature ofthese compounds. Suifice it to say that the formation of such compoundsaccounts partly for the fact that the size of the particles of the finalalloy is, in general, much smaller and more uniform than the powderedoxide and powdered metal of the initial mixture.

It will be understood by those skilled in the art that the length oftime that the heat treatment second group in powdered form, raising thetemperature of the mixture to the point where the hydrogen is liberatedfrom the calcium hydride, the liberated hydrogen reducing the metaloxide whereupon the calcium combines with the oxygen to form calciumoxide, and thereafter further raising the temperature to the point wherethe metal liberated from the oxide diifusesinto the alloying elementfrom the second group.

2. The process of forming powdered alloys consisting of a metal selectedfrom a first group consisting of titanium, zirconium, tungsten, hafnium,thorium, tantalum, uranium, molybdenum, chromium and beryllium and analloying element selected from a second group consisting of titanium,zirconium, tungsten, hafnium, thorium, tantalum, uranium, molybdenum,chromium, beryllium, carbon, iron, nickel and cobalt which cium hydride,barium hydride and strontium hytemperature of the mixture to liberatedfrom the second group. V

3. The process according to claim 1 in which the amounts of powderedoxide and alloying elements are varied in accordance with the desiredpercentages in the final alloy whereas the amount of'calcium hydride isvaried'in accordance with the amount of the metal oxide present.

according to claim 2 in which after difiusion of the PETER- P.ALEXANDER.

